where do I acquire replacement screws JIS for a 64 305

[Tim Miller]

That's simple....some of use like original 5 X .90 and not cross threading with a 5x.80 tap. Of course that's me and my nos screw stash talking.Lol. BTW the 5x.90 tap is available from McMaster Carr in Irwin #26317 set.

Tim

Just a simple question.
What's the big deal of staying with JIS threads?
The screws are rather difficult to find and when replaced with the ISO no one can tell the difference. ....................lm

Ok now I get it. I do have JIS screws and JIS thread.

Then back to the original question - where can I get a JIS tap for the threaded hole that has been messed up?

Here's a set that covers all of the possibilities (i.e. JIS and ISO) https://www.craftsman.com/products/craf ... ap-die-set. There are other smaller sets on the site so it's worth checking out.

Bill Silver in his Restoration Reference Guide reproduces a service bulletin titled Change of Threaded Parts. It's dated 1967 so there should be few bikes with ISO (also called modified JIS) threads. Most of the sizes are unaffected by the change.

Here's the table from the bulletin showing the affected sizes.

Code: Select all

Diameter    Old JIS pitch    Modified JIS (ISO) Pitch
3mm          0.6                  0.5
4mm          0.75                0.7
5mm          0.9                  0.8
12mm        1.5                  1.25

It looks like there is enough old machinery out there to make the old-sized taps and dies desirable.

[Tim Allman]

Just a simple question.
What's the big deal of staying with JIS threads?
The screws are rather difficult to find and when replaced with the ISO no one can tell the difference. ....................lm

If few threads are engaged maybe you can get away with the wrong thread pitch but it is still the wrong pitch and all that comes with the mismatch. If there was no way of getting the right screws I might consider your solution but frankly, I'm surprised you are suggesting it as a reasonable way of dealing with the problem.

[jkv357]

OK, so this has been bothering me.

I took the screw out of my '64 Dream's dynamo cover and took it over to the Machine Shop next door to measure the tread pitch.

I was wrong.

Tim is correct. The screw is 5mm with a pitch of .9mm - like he posted.

[pemdoc65]

I have used a 5x0.9 die to rethread the 5x0.8 screws for my generator cover that I ordered from David Silver several years ago. I know that it is not perfect, but the screws thread in nicely and have remained tight. The other option is to retap the hole to a 5x0.8 thread. I purchased both taps and dies in on ebay so I would have the option of doing either.

[LOUD MOUSE]

I've been restoring and making others run for other folks for years and this JIS thread problem has not improved over that time which caused me to "See what would happen if I tapped to the ISO thread".
Well "Because I'm not afraid to tap to the ISO I found that "THE THREADS ARE ABLE TO HOLD THE SCREW WITH NORMAL PRESSURE". (same as the JIS)
What is the impact for a restoration.
YA CAN'T TELL WHAT THREAD THE SCREW IS"!
Locations like the points area, lever perches and head light rim can be installed with screws from any normal hardware store and all ya need to do is get/have the ISO tap.
For the perches I grind the end of the tap sort of flat to get as many threads without coming out the side.
Try this TIM and ya may be surprised how simple and cost and time effective this is. .................lm

Just a simple question.
What's the big deal of staying with JIS threads?
The screws are rather difficult to find and when replaced with the ISO no one can tell the difference. ....................lm

If few threads are engaged maybe you can get away with the wrong thread pitch but it is still the wrong pitch and all that comes with the mismatch. If there was no way of getting the right screws I might consider your solution but frankly, I'm surprised you are suggesting it as a reasonable way of dealing with the problem.

[Tim Allman]

I've been restoring and making others run for other folks for years and this JIS thread problem has not improved over that time which caused me to "See what would happen if I tapped to the ISO thread".
Well "Because I'm not afraid to tap to the ISO I found that "THE THREADS ARE ABLE TO HOLD THE SCREW WITH NORMAL PRESSURE". (same as the JIS)
What is the impact for a restoration.
YA CAN'T TELL WHAT THREAD THE SCREW IS"!
Locations like the points area, lever perches and head light rim can be installed with screws from any normal hardware store and all ya need to do is get/have the ISO tap.
For the perches I grind the end of the tap sort of flat to get as many threads without coming out the side.
Try this TIM and ya may be surprised how simple and cost and time effective this is. .................lm

You weren't clear. I understood you to mean that you were just forcing the screws. What you are describing here is obviously a much better solution.

And, please don't yell.

[DJM]

I found 5mm x 0.9mm screws here in the UK, plenty of normal round heads, the guy didn't have the oval heads as used on the alternator and points covers but I think he has those now too.

If you're interested I'll see if I can dig out his details.